Method and apparatus for producing an oil reservoir

ABSTRACT

A method for producing an oil reservoir, comprising establishing an oil producing well, producing a production fluid containing oil and water, transporting the production fluid to a downhole liquid/liquid hydrocyclone, separating the fluid in the liquid/liquid hydrocyclone into an oil enriched stream at the hydrocyclone underflow, transporting the oil enriched stream to the surface, reinjecting the water enriched stream at a downhole site, cooling the transported oil enriched stream by sending a counterflow of a cooling medium relative the oil enriched stream, thereby keeping the oil enriched stream in a substantially liquid phase.

FIELD OF INVENTION

The present invention relates to a method and an apparatus for producingan oil reservoir. The invention is developed in connection with thedemand and need for production of deeper localized and mostly relativelysmall oil reservoirs. When producing such oil reservoirs it is regularlynecessary to inject water in the resevoir thereby forcing out thehydrocarbons from the reservoir.

BACKGROUND

Increasingly, oil producers are looking for ways to produce oil fromwells in which the production fluid has a high water cut efficientlyenough to make the cost of production economic. One known method is toseparate the production fluid in a downhole separator comprising one ora series of hydrocyclones in order to provide initial separation of atleast some of the water from the production fluid to reduce the quantityof production fluid which needs to be transported to the surface. Theseparated water is re-injected, to the oil reservoir or another site.

SUMMARY OF INVENTION

According to the present invention a method for producing an oilreservoir is provided,

comprising establishing an oil producing well,

producing a production fluid containing oil and water,

transporting the production fluid to a downhole liquid/liquidhydrocyclone,

separating the production fluid in the liquid/liquid hydrocyclone intoan oil enriched stream at the hydrocyclone overflow, and a waterenriched stream at the hydrocyclone underflow,

transporting the oil enriched stream to the surface,

re-injecting the water enriched stream at a downhole site, and

cooling the transported oil enriched stream by sending a counterflow ofa cooling medium relative the oil enriched stream, thereby keeping theoil enriched stream in a substantially liquid phase.

By cooling the ascending oil enriched stream the stream liquid phase iskept as long as possible, thereby substantially avoiding gas formation.

When producing a reservoir containing volatile oils the production fluidwill be subject to a volatilazation caused by a pressure reductionupwards in the well. A cooling of the upwards flowing upstream in thewell will cause a temperature reduction balancing the pressurereduction, whereby the condensation curve in the corresponding phasediagram is not crossed. Thus gas will not evolve and a multi-phasesituation is avoided. The result is a preventive liquidation in that thestream is hindered in giving away the volatile heat and will remain inthe same phase, that is the liquid phase. Some of the most volatilecomponents will of course evolve and remain in the gaseous phase bit itis estimated that the bulk of the gas phase will not evolve but remainin the liquid.

The counterflow may advantageously be used as the driving medium for apump transporting the oil enriched stream.

The cooling medium may preferably include injection water, deliveredfrom a water pump at or above the surface.

Provided the cooling is not sufficient to avoid a disturbing gas phasethe oil enriched stream can be pressurized in one or more additionaldownhole pumps positioned in the well above the transportation pump.Thereafter the stream is cooled further, striving to keep the streamoutside the condensation line in the phase diagram.

The cooling medium may include re-injection water provided from anaquifier, i.e. an underground site containing water. Water drawn from anaquifier is preferably separated in a downhole solid/liquidhydrocyclone, whereby the separated water is re-injected in theproducing reservoir and the solids are re-injected in the ground, forinstance in the aquifier.

The present invention also provides an apparatus for producing an oilreservoir, the apparatus comprising a downhole liquid/liquidhvdrocyclone for separating production fluid containing oil and waterinto an oil enriched stream and a water enriched stream, a downhole pumpfor pumping the oil enriched stream to the surface, and means forsending a counterflow of cooling medium relative the oil enrichedstream.

The means for sending the counterflow may preferably include a means forsending a flow of injection water down the well.

Preferably the downhole transporting pump may be in driven connectionwith a downhole injection water driven turbine.

Also a re-injection water pump may preferably be in driven connectionwith said downhole turbine.

As disclosed above in connection with the inventive method the apparatuswill preferably include one or more additional downhole pumps fortransport (pressurizing) of the cooled oil enriched stream.

The apparatus may further include a downhole solid/liquid hvdrocyclonein the well at a position above the downhole transport pump, saidhydrocyclone being flow coupled to an aquifier by means of a pump andhaving an overflow delivering separated water down to the oil producingreservoir, and an underflow delivering separated solids to anunderground site.

BRIEF DESCRIPTION OF DRAWING

The invention will now be described with reference to the drawings, inwhich:

FIG. 1 is a schematic diagram of an apparatus according to theinvention,

FIG. 2 is a schematic diagram of another apparatus according to theinvention, and

FIG. 3 is a schematic phase diagram illustrating the basic inventiveidea.

DETAILED DESCRIPTION OF EMBODIMENTS

As shown in FIG. 1, a well 1 penetrates into a production formation 2. Adeviation well 3 is used for the production of oil from the formation orreservoir 2. A production flow 46 (see FIG. 2) from the well 3 istransported to a series of liquid/liquid downhole hydrocyclones 4 wherethe production flow is separated in an oil enriched stream 42 from theoverflows and a water enriched stream from the underflows. A downholepump 5 provides for the transport of the oil enriched stream 40 up tothe surface (here a sea bottom) through a flow tube 6. At the surface 7the oil enriched stream goes through a flexible riser 8 to a productionvessel 9.

Injection water provided by an injection pump 10 at the surface 7 isforced down the well 1 in the annulus 12 between the flow tube 6 and thesurrounding well wall, as indicated with the arrows 11.

The transport pump 5 is part of a downhole unit consisting of the pump5, a water driven turbine 13 and an injection water pump 14, both pumps5 and 14 being in drive connection with the turbine 13. The water pump14 takes separated water 44 from the hydrocyclones 4 and deliver it tothe space 15, delimited by the two packers 16 and 17 in the well 1. Fromthis space 15 the water is re-injected through the injection line 18which penetrates into the formation 2.

The injection water 11 from the surface pump 10 is used as a drivemedium for the turbine 13 and is expelled into the space 15, wherefromit is injected through the injection line 18.

The injection water 11 which flows down the annulus 12 is used as acooling medium for the oil enriched stream flowing upwards through thetube 6.

In the tube 6 there is indicated an additional stream pump which is usedfor pressurizing the oil enriched stream.

Additional cooling may be added by means of a cooler 20 which is servedby a refrigeration plant 21, for instance using Freon as refrigeratingmedium. It is not shown but the cooler 20 may preferably be of a typehaving a double jacket where the refrigerating medium flows downcountercurrently to the ascending oil enriched stream and then flowsback up radially outside the descending flow.

FIG. 2 depicts schematically a possible apparatus including a downholere-injection pump 22, the inlet of which being connected to an aquifier23 (a water containing formation) and the outlet of which beingconnected to the inlet of a downhole solid/liquid hydrocyclone 24. Inthis hydrocyclone 24 the water from the aquifier is separated in solids,which flows through a line 50 from the underflow and back to the aquiferformation 23, and re-injection water 52 which flows down forre-injection in the oil producing formation 2. As in FIG. 1 a productionflow goes from the formation 2 to downhole hydrocyclones 4 where theproduction fluid is separated as disclosed above in connection with theapparatus in FIG. 1. The cooling of the oil enriched stream which istransported up through the line 6 (transport pump 5 omitted in FIG. 2)is not disclosed in FIG. 2.

The object of FIG. 2 is to disclose the possible inclusion of there-injection unit 22, 24 and to show a possible adding of chemicals tothe re-injection water through a supply line. Such chemicals may beviscosity reducing additives etc. Such chemicals may be added to the oilenriched stream in the tube or line 6 but the adding as shown to there-injection waters bears the advantage that the chemicals will remainunderground because they are recirculated in the system in anenvironmental friendly manner.

The basic inventive idea is shown in FIG. 3, which is a schematicalphase diagram for the oil. In the pT diagram the point 1 may be taken asa starting point. A pressure reduction would result in a moving to point5 in the phase diagram, with corresponding formation of a gas phase, say40% gas and 60% oil. By cooling the stream means following the line tothe point 2, i.e. at or above the condensation line c, and further downto point 4. At point 2 a pressurizing in the additional pump 19 (conf.FIG. 1) will lift the position in the diagram to point 3, wherefrom afurther cooling will result in point 6 on the condensation line, insteadof point 4, as indicated in FIG. 3.

The effective cooling area and the mean temperature difference arefavorable in the system according to the invention. The cooling area ina 3000 meter deep well will for instance be around 1000 square metersgiven a 4″ tube, and the mean temperature difference will be up to 50degrees C., which will represent an adequate cooling effect.

What is claimed is:
 1. A method of producing an oil reservoir,comprising establishing an oil producing well, producing a productionfluid containing oil and water, transporting said production fluid to adownhole liquid/liquid hydrocyclone, separating the production fluid inthe liquid/liquid hydrocyclone into an oil enriched stream at thehydrocyclone overflow, and a water enriched stream at the hydrocyclioneunderflow, transporting the oil enriched stream to the surface,reinjecting the water enriched stream at a downhole site, cooling thetransported oil enriched stream by sending a counterflow as a coolingmedium relative to said oil enriched stream, thereby keeping the oilenriched stream in a substantially liquid phase, wherein said coolingmedium is injection water.
 2. A method as in claim 1, using saidcounterflow of cooling medium as a driving medium for a pumptransporting said oil enriched stream.
 3. A method as in claims 1 or 2,adding additional transportation energy to the oil enriched stream,thereby keeping the cooled oil enriched stream in a substantially liquidphase.
 4. A method as in claim 1 or 2, said cooling medium includingre-injection water provided from an aquifer.
 5. An apparatus forproducing an oil reservoir through an oil producing well, the apparatuscomprising a downhole liquid/liquid hydrocyclone for separating aproduction fluid containing oil and water into an oil enriched streamand a water enriched stream, a downhole pump for pumping said oilenriched stream to the surface, and means for sending a counterflow of acooling medium relative to the surface pumped oil enriched stream.
 6. Anapparatus as in claim 5, said means for sending said counterflowincluding a means for sending a flow of injection water down said well.7. An apparatus for producing an oil reservoir through an oil producingwell, the apparatus comprising a downhole liquid/liquid hydrocyclone forseparating a production fluid containing oil and water into an oilenriched stream and a water enriched stream, a downhole pump for pumpingsaid oil enriched stream to the surface, and means for sending acounterflow of a cooling medium relative to the surface pumped oilenriched stream, said means for sending said counterflow including ameans for sending a flow of injection water down said well, including adownhole turbine driven by the injection water, said turbine being indrive connection with said downhole pump.
 8. An apparatus as in claim 7,including a downhole re-injection water pump in drive connection withsaid downhole turbine.
 9. An apparatus as in claim 8, including anadditional downhole pump for transport of said cooled oil enrichedstream to the surface, said additional pump being arranged in said wellat a position between the said downhole pump and the surface.
 10. Anapparatus as in any of the claims 6-9, including a downhole solid/liquidhydrocyclone in the well at a position above said downhole pump, saiddownhole solid/liquid hydrocyclone having an inlet, an overflow and anunderflow, said inlet being connected with an aquifer, said overflowejecting re-injection water down the well to the reservoir, and saidunderflow ejecting solids enriched liquid to a downhole site, preferablyto said aquifer.
 11. An apparatus for producing an oil reservoir throughan oil producing well, the apparatus comprising a downhole liquid/liquidhydrocyclone for separating a production fluid containing oil and waterinto an oil enriched stream and a water enriched stream, a downhole pumpfor pumping said oil enriched stream to the surface, and means forsending a counterflow of a cooling medium relative to the surface pumpedoil enriched stream, including a downhole solid/liquid hydrocyclone inthe well at a position above said downhole pump, said downholesolid/liquid hydrocyclone having an inlet, an overflow and an underflow,said inlet being connected with an aquifer, said overflow ejectingre-injection water down the well to the reservoir, and said underflowejecting solids enriched liquid to a downhole site, preferably to saidaquifer.